Collision warning, avoidance, and countermeasure systems are becoming more widely used. Collision warning systems are able to detect an object within proximity of a host vehicle and assess whether the object detected is an obstacle and poses a threat to the host vehicle. These systems also provide a vehicle operator knowledge and awareness of obstacles or vehicles within a close proximity in time such that the operator may perform actions to prevent colliding with the detected obstacles. Countermeasure systems exist in various passive and active forms. Some countermeasure systems are used in the prevention of a collision, and others are used in the prevention of an injury to a vehicle operator.
Collision warning systems may be forward or rearward sensing. These systems can indicate to a vehicle operator that an object, which may not be visible to the vehicle operator, is within a stated distance and location relative to the host vehicle. The vehicle operator may then respond accordingly. Other collision warning systems and countermeasure systems activate passive countermeasures such as air bags, load-limiting seat belts, or active vehicle control including steering control, accelerator control, or brake control whereby the system itself aids in preventing a collision or injury.
Many countermeasure systems require knowledge of locations and velocities of objects or vehicles that are proximate to a host vehicle. Global Navigation Systems (GNS), such as the United States Global Positioning System (GPS) and other similar systems that are based on similar principles, such as the Russian Federation Glasnost system, the People's Republic of China Beidou (Big Dipper) system, and the European Union Galileo system can provide this information, but frequently without the necessary accuracy.
A typical GPS vehicle scenario includes multiple vehicles equipped with GPS receivers that are coupled to onboard computers equipped with two-way digital radios for communications therebetween. Position, velocity, and time (PVT) data is computed in the GPS receivers and passed to the computers. The PVT data may be exchanged between the vehicles using the two-way radios, or through use of wireless modems or network devices. Several protocols are established for performing this exchange of PVT data, which includes Dedicated Short Range Communications (DSRC) and Institute of Electric and Electronics Engineers (IEEE) 802.11a specification protocols. A typical or normal GPS calculates PVT data using the time of travel of signals from a system of satellites to a GPS receiver. In this process many of the user errors attributable to GPS measurements are eliminated. However, the errors attributed to the GPS receivers cannot be eliminated by such a subtraction and the errors, as a result, are multiplied or amplified in determining position. The size of these errors is sensitive to the geometric relationship between GPS satellites being used.
Additionally, in using current GPSs, each vehicle's GPS must be able to receive signals from at least four satellites simultaneously for the proper functioning thereof. Buildings, overpasses, foliage, and terrain may limit the number of satellites that are “visible” to the receivers of a GPS. Thus, these limitations reduce the effectiveness of current GPSs in determining vehicle PVT data for the purposes of vehicle safety, navigation, and telematics.
Thus, there exists a need for an improved system for determining relative positioning and velocity data for an automotive vehicle that minimizes the above-stated errors and is not limited by the number of visible GPS satellites.